1. Field of the Invention
The present invention relates to a display device. More particularly, the present invention relates to a liquid crystal display having high color saturation.
2. Description of Related Art
Thin film transistor liquid crystal displays (TFT-LCD) have become a mainstream product in the display market due to high image quality, great space efficiency, low power consumption and no radiation. To achieve high-fidelity color reproduction, cold-cathode fluorescent lamps (CCFL) are used as backlighting for computer and TV monitors. According to the NTSC (National Television System Committee) color television standard, liquid crystal displays using CCFL can achieve an NTSC ratio of 72% and above. However, the color saturation of liquid crystal displays utilized in handheld or portable devices such as cell phones is still unsatisfactory. Conceivably, to satisfy users' ever-increasing needs, all manufacturers focus on developing high-fidelity color reproduction techniques. Further, the development of high-fidelity color reproduction techniques is primarily related to the backlight module of liquid crystal display and the color filter substrate.
In the development of high-fidelity color reproduction techniques, the type of backlight modules used is critical. At present, white light emitting diodes (LED) are used the most commonly as backlighting. It is because white LEDs are compact, non-toxic, driven by direct current and simple in construct. Moreover, white LEDs have fast response time and long lifetime. As a result, white LEDs have been widely used in backlight modules for portable devices. Currently, in most white LED backlight modules, the white LED includes a blue LED chip and yttrium aluminum garnet (YAG) phosphor. However, the color rendering property of this type of white LED is poor. More specifically, as the NTSC ratio of a liquid crystal display increases, the luminance of the liquid crystal display decreases drastically. Hence, another type of white LED has been developed, which utilizes red, green and blue LED chips for emitting light (e.g. red, green, and blue light) of different wavelengths. This type of white LED can easily increase the NTSC ratio of a liquid crystal display. On the other hand, the white LED utilizing red, green and blue LED chips simultaneously is bulky and high-cost. Additionally, the control circuitry for driving the red, green and blue LED chips is complex. Consequently, conventional liquid crystal displays cannot achieve high color saturation due to the limited volume of the existing backlight module and the simplicity of the existing control circuitry.